Abstract

Ni-based superalloys are metallic materials with exceptional combinations of creep and oxidation
resistance at high temperatures. Wrought alloys are hot formed at high temperatures and
subsequently annealed and aged. The final mechanical properties of the alloys are a combination
of the grain size generated during the process and the precipitation state after aging. In fact,
precipitation phenomena are complex for these alloys, which contain up to 12 different elements
in their compositions. This study will deal with the forming characteristics of Haynes 242. Prior to
forming, usually by forging, the material has to be reheated and this initial thermal treatment can
affect grain size. The reheating stage is defined by the temperature and soaking time at the
selected temperature. The best combination of these two parameters has to warranty that forging
will be performed above the solvus temperature of precipitates without promoting excessive grain
growth. The initial part of the study will analyse the effect of different temperatures and soaking
times on the grain size and precipitates. After reheating, forging operations are performed at
different forming temperatures and strain rates. Forging conditions will be simulated by means of
hot compression testing. Compression samples will be first reheated according to the optimal
conditions defined in the first part of the study, and then compressed at different temperatures
and strain rates. Hot flow curves will be obtained which will be used for the analysis of the hot flow
behaviour of the alloy. Metallographic evaluation of the compressed samples will assess the
evolution of the grain size during forming and the mechanisms taking place, i.e. dynamic
recrystallization or dynamic recovery, according to the deformation parameters. These results will
be useful for the assessment of hot deformation operations (reheating and forging conditions) for
Haynes 242, leading to fine and homogeneous microstructures.